Wireless communication platforms, for example, communications satellite systems, are transitioning from point-to-point high-capacity trunk communications between large, costly ground terminals to multipoint-to-multipoint communications between small, low-cost ground stations. The development of multiple access techniques has facilitated this transition. Using a multiple access technique, independent signals can be combined on a communication channel at a transmitter and split up at a receiver by a demultiplexer. The communication channel may be shared between the independent signals in one of several different ways, such as time division multiplexing, frequency division multiplexing, and code division multiplexing, or a combination thereof.
A multiple access technique known as frequency reuse allows a communication platform to communicate with a number of these ground stations using the same frequency, i.e., communication channel, by simultaneously transmitting packets of information over a finite number of steerable beams pointed toward each of the ground stations. Since each of the beams is operating at the same frequency, the beams cannot be allowed to illuminate the same region of the earth at the same time. If the beams do illuminate the same region at the same time, i.e., the beams overlap, interference between beams can occur. Unfortunately, the overlapping signals may illuminate unintended receivers and may interfere with their signal reception.
Beam interference may be due to the level of radiated energy outside of the regions the beams are intended to illuminate. The amount and direction of this overflow of radiated energy is in turn due to planned and unplanned consequences. In a satellite-based communication platform, some of these consequences can include oversizing of the beam to accommodate continuous satellite motion, beam shape changes due to beam angles (i.e., beam shape changes from circular to elliptical based on beam angle relative to nadir), beam shape changes due to thermal and aging factors in the transmission equipment, and time varying changes relative to the attitude angles of a satellite.
The problem of beam interference may be mitigated or prevented by effective transmission resource allocation strategies. An effective transmission resource allocation strategy is one in which, packets of data to be transmitted from a communication platform are scheduled for transmission in a time and resource efficient manner, while concurrently avoiding circumstances in which interference between transmissions from two or more beams could occur. When attempting to mitigate the problem of beam interference, communication platforms typically consider four variables for each transmitted packet. These four variables include quality of service (QOS), spatial separation, time separation, and transmission resource assignment.
The QOS is a measure of the quality of the communication service provided to a subscriber and may be quantitatively indicated by system performance parameters such as signal to noise ratio, bit error ratio, message throughput rate, call blocking probability, and so forth. QOS is a crucial variable in the processing of a packet because QOS drives system performance. That is, certain data packets may demand a higher QOS than other data packets. For example, realtime voice and video communication are highly intolerant of latency, or transmission delays within the network, and may demand a higher QOS. In contrast, non-realtime data files can tolerate some transmission delay and a lower QOS in terms of latency.
Spatial separation indicates the physical separation requirements, with respect to the earth, between individual beams to prevent beam interference. Time separation indicates the separation in time between the transmission of packets. Transmission resource assignment indicates the allocation of a particular beam for transmission of a packet. In order to effectively schedule packets for transmission, all four of these variables should be considered.
One prior art method for packet transmission scheduling is a four variable processing for a common queue technique. In other words, packets are scheduled to transmission resources by concurrently considering QOS, spatial separation, time separation; and transmission resource availability. Unfortunately, such processing is extremely complex and requires significant and costly realtime processing capability.
Another prior art method for packet transmission scheduling is an individual beam resource queue technique. In such a technique, packets are allocated to particular transmission resources in a first processing stage. QOS and time separation are then considered in a second stage of processing. Spatial separation is considered in a final processing stage. While the complexity of the processing is somewhat reduced from the first prior art technique by separating the processing of the variables into three stages, the final processing stage is performed iteratively which undesirably increases the processing time, cost, complexity.
Accordingly, what is needed is an efficient packet scheduling method and system for solving multiple variable resource allocation problems in a wireless communication platform. Furthermore, what is needed is a packet scheduling method and system which consider QOS as the highest priority of the processing variables.